Evaluation of soft tissues simulant materials in cone beam computed tomography

Prior research has shown that simulating soft tissues in imaging studies is crucial for accurate diagnostic training and phantom development. However, no prior work had resolved the specific impact of different simulant materials on pixel intensity values in cone beam computed tomography (CBCT). While it was already known that materials like wax and gelatin are used in phantoms, the extent to which they affect pixel intensity remained unclear. This gap motivated the need to evaluate how these materials compare to a gold-standard. Researchers had not yet established which simulant most closely mimics soft tissues in CBCT. Existing methods lacked a direct comparison of ice, wax, and gelatin in this context. The uncertainty around material effects on pixel intensity values in dental and bone regions drove this investigation. This study aimed to clarify how these simulants influence CBCT outcomes.

The aim of this study was to assess how different soft tissue simulant materials affect pixel intensity values in CBCT imaging. Specifically, the researchers wanted to compare ice, modelling wax, and ballistic gelatin against a gold-standard of intact soft tissues. The motivation was to identify which material most closely replicates true soft tissue behavior in CBCT scans. By measuring pixel intensity values in dental, bone, and soft tissue regions, the study sought to determine material-specific effects. The researchers also aimed to evaluate whether the location—mandible or maxilla—impacted these effects. This information is essential for developing accurate phantom models in dental imaging. The study focused on mean pixel intensity values and their standard deviation across regions. The ultimate goal was to inform best practices in phantom design for CBCT applications.

The study used three piglet heads with intact soft tissues as the gold-standard. Simulant materials—ice, modelling wax, and ballistic gelatin—were applied with the same thickness as the original tissues. CBCT images were acquired for each group and compared to the gold-standard. Pixel intensity values were measured in dental, bone, and soft tissue regions. Analysis of variance was used to compare mean pixel intensity values across groups. Dunnet's test was applied to compare simulants against the gold-standard. Pearson's correlation and linear regression were used to assess relationships. The researchers evaluated differences in pixel intensity values in the mandible and maxilla separately.

The simulant materials did not significantly alter the mean pixel intensity values of teeth compared to the gold-standard (p = 0.1017). Only ice affected the mean pixel intensity of bone (p = 0.0156). Modelling wax and ice changed the mean pixel intensity of soft tissue regions (p = 0.001 and p = 0.0076, respectively). Ballistic gelatin did not significantly alter soft tissue pixel intensity (p = 0.5814). Differences in pixel intensity were significant only in soft tissue regions when comparing mandible and maxilla. Standard deviation was not significantly influenced by any simulant (p > 0.05). Ballistic gelatin showed the lowest variability in pixel intensity values. It was identified as the best soft tissue simulant due to minimal impact on pixel intensity across all regions.

The authors concluded that ballistic gelatin is the most suitable material for simulating soft tissues in CBCT imaging. It had the least influence on mean pixel intensity values in all regions compared to the gold-standard. Ice altered bone pixel intensity values but not dental ones. Modelling wax and ice affected soft tissue pixel intensity, while gelatin did not. The location—mandible or maxilla—only influenced soft tissue regions. Standard deviation was not significantly affected by any simulant. Ballistic gelatin showed the lowest variability in pixel intensity values. These findings suggest that gelatin is preferable for phantom development in CBCT studies. The authors propose that gelatin should be prioritized in future phantom designs for dental imaging.